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Chapter 40
The Stars
40.1 Constellations
• How many stars do you think the unaided eye can
see?
– Only about 3000
• Do stars look different through a telescope?
– No, even with a telescope, stars are still just points of
light
• Why?
– Because stars are so far away
– Brightest are 10 to 1000 light-years away (1 light-year =
9.5 x 10^12 km= 9,500,000,000,000)
– Pluto is 59.2 million (59,200,000) miles away
Constellations
• Early astronomers grouped stars into
constellations
• Constellations don’t move, but we move
– Causes night sky to vary
Can you identify the
constellation?
What star is
this?
40.2 Birth of Stars
• Interstellar dust spread out around space
– Allows particles to condense to form star
– Similar to cloud formation
• Formation
– Huge cloud of low-temp material
– Gravity attracts other particles
– Eventually have a protostar- a forming star more
massive than the sun and bigger than our solar
system
Beyond a Protostar
• Gravity causes ball to contract and increases
temperature and pressure
• At over 10 million Kelvins (18 million
Fahreheit), hydrogen nuclei fuse to helium
– Thermonuclear reaction
– Releases tons of energy, stops contraction
• Outward radiation and gas pressure =
inward gravitational pressure = stable star
Composition of Stars
• Material in stars depends on how old they
are
– Older stars had only hydrogen and helium
– Elements heavier than hydrogen and helium
came from the core of stars
– When stars die, they spew material out
– Newer stars are composed of heavier elements
– We are made of star dust!
40.3 Life and Evolution of
Stars
• Life span depends on how fast a star burns its
fuel
– Does a gallon of gas last longer in a truck or a car?
– Similar in stars…smaller stars burn longer
• Calculate mass of stars using binary stars
– Binary stars revolve around each other
– Observing them relative to each other gives us mass
– Some think Sun might have a binary…Nemesis
40.4 Death of Stars
• How are stars fueled?
– Nuclear fuel
– Fusion of hydrogen to helium
• Average mass stars like our Sun
– Contract and raise temperature
– Ignites the hydrogen and helium to produce a
red giant
– Our sun will reach that stage in 5 billion years
Death of Stars
• Stars smaller than the sun
–
–
–
–
No source of nuclear energy so they shrink
Shrink and form expanding shells
These form planetary nebula
Core is white hot….a white dwarf
Fades into a black dwarf
If it has a binary, pulls
hydrogen from there
and creates a nova
The Ant Nebula, a cloud of dust and gas whose
technical name is Mz3, resembles an ant when
observed using ground-based telescopes. The
nebula lies within our galaxy between 3,000 and
6,000 light years from Earth.
In third place is Nebula NGC 2392, called Eskimo
because it looks like a face surrounded by a furry
hood. The hood is, in fact, a ring of comet-shaped
objects flying away from a dying star. Eskimo is 5,000
light years from Earth.
Starry Night, so named because it reminded
astronomers of the Van Gogh painting. It is a halo
of light around a star in the Milky Way.
In sixth place is the C one Nebula. The part
pictured here is 2.5 light years in length (the
equivalent of 23 million return trips to the
Moon).
40.5 Supernova
• Star life cycle depends on its mass
• Larger Stars produce more heat
– Don’t become white dwarfs
– Fusion occurs until Iron is formed
– Eventually starts to collapse
Final Collapse
• Collapse, explosion, and remnant timeline?
• Explosion creates heavier elements like gold,
silver, and lead
• Called a supernova
• Supernova so bright, they can even be seen
by day
Neutron Stars
• Inner part of supernova implodes
– Compressed the core
– Creates neutron star
• Neutron stars:
– Spin at great speeds
– Create pulsars – low-frequency radio emissions
40.6 Black Hole
• Largest stars have no force strong enough to
stop them from contracting
• Collapse until they disappear from
observable universe…a black hole
• Speed of collapse increases until it is faster
than the speed of light, therefore we can’t see
anything!
40.7 Galaxies
• Galaxy = large group of stars, planetary
nebulae, and interstellar dust
• How many stars do you think make up the
Milky Way Galaxy?
– 200 billion
– Seen as a faint band of light across the sky
• Most striking feature of Milky Way is spiral
arms = hot, blue stars, and clusters of young
stars
Elliptical Galaxies
• Most common
• Dim, so most difficult to see
• Have little gas and dust, so cannot create
new stars
Irregular Galaxies
• Small and faint
• Large clouds of gas and dust
Spiral Galaxies
• Most beautiful
• Lots of newly formed stars
• 2/3 of all KNOWN galaxies
– Only 15 to 20% of all galaxies
– Elliptical more common, just harder to see